The presently disclosed embodiment relates to magnetrons that oscillate microwaves, and particularly to a structure of coaxial magnetrons having an outer cavity outside an anode resonant cavity.
Since magnetrons can oscillate high-power microwaves efficiently in a simple configuration, they have been used in a variety of applications and devices. Among those, examples of devices in which an oscillation frequency needs to be tuned precisely include radars that execute detection by changing a frequency precisely to avoid interference and Linac that puts precisely-tuned microwaves into a narrow band resonator with a high Q factor to apply an accelerating electric field to an electron. Magnetrons used in such applications and devices need to have a mechanism that can mechanically change frequencies. Coaxial magnetrons are put into practical use as one option.
FIG. 6 shows an example of a coaxial magnetron in which high-power microwaves are obtained. As shown in FIG. 6, around a cathode 1 disposed centrally, vanes 2 radially disposed and an anode cylinder 3 to which the vanes 2 are joined as an anode are provided, and the vanes 2 and the anode cylinder 3 form an anode resonant cavity 50. A slot 4 is provided in the anode cylinder 3 and a cylindrical side body 6 is disposed around the anode cylinder 3, thereby forming an outer cavity 60 coaxial with the anode resonant cavity 50. Furthermore, pole pieces 7a and 7b are disposed above and below the cathode 1, a tuning piston 8 is provided in the outer cavity 60, and a cooling passage 11 for running a coolant therethrough is provided in an input side structure 14 to be joined to an input part 9.
The pole piece 7b is provided as a part of an upper structure 12, and the upper structure 12 is joined to the cylindrical side body 6, thus assembling the magnetron. The anode cylinder 3 is joined to the input side structure 14 but not to the upper structure 12, and is cantilevered.
In this configuration, the resonance frequency and oscillation frequency of the magnetron can be adjusted by moving the position of the tuning piston 8 from outside and changing the reactance of the outer cavity 60. As a result, the oscillation frequency of the magnetron can be changed precisely, and tuned to a frequency required for an application or a device. The magnetron can oscillate high-power microwaves, and can be designed to generate high-power microwaves with the peak output of several MW and the average output of several kW.
While a high oscillation efficiency can be achieved in such an exceedingly high-power magnetron, it is important to design a cooling function for heat generated by anode dissipation. In addition, since the vanes 2 are made of a thin metal finely, when an overheat happened, there was a case where deformation was caused, thereby affecting oscillation characteristics or melting deformation was caused, thereby deteriorating the function of the magnetron. Therefore, for high-power magnetrons, there was a proposal of a design such that a coolant is run in the vicinity of an anode structure for cooling. In the case of FIG. 6, the cooling passage 11 is provided in the vicinity of the anode cylinder 3 to cool the magnetron.
JP 2004-134160 A describes a magnetron using a coolant, though it is not a coaxial magnetron, In this example, a cooling jacket is provided along the circumferential direction of the outer wall surface of an anode cylinder to which vanes are joined, and a coolant is run through the cooling jacket. This configuration enables heat generated around the vanes by anode dissipation to be exchanged with the coolant efficiently, which leads to the decrease of the temperature of the anode including the vanes.
However, as can be seen from the configurations shown in JP 10-269953 A and JP 10-302655 A, the coaxial magnetrons as shown in FIG. 6 are configured such that the outer cavity 60 is provided outside the anode cylinder 3 and the tuning piston 8 is moved up and down therein. Therefore, the configuration of the cooling jacket as described in JP 2004-134160 A cannot be adopted, and there is a problem that the magnetron cannot be cooled efficiently.
Meanwhile, in the coaxial magnetrons, the anode cylinder 3 is joined to only the input side structure 14 and is cantilevered as described above. Therefore, there was a problem that heat release to the outside from the anode cylinder 3 cannot be carried out satisfactorily. In other words, in order to strictly secure the distance between the opposing pole pieces 7a and 7b, as shown in FIG. 6, magnetrons are generally designed so that the length of the anode cylinder 3, which may be a cause of an error, is set to be rather short and only one end of the anode cylinder is joined and the other end of the anode cylinder on the side of the upper structure 12 is free. In assembling, the distance between the pole pieces 7a and 7b is adjusted to a predetermined dimension by accurately adjusting the distance La between the input side structure 14 and the upper structure 12 to a specified value and joining the upper structure 12 to the cylindrical side body 6. For this reason, the anode cylinder 3 is joined to the input side structure 14 and held in a cantilevered state and the other end of the anode cylinder on the side of the upper structure 12 is free. As a result, heat release from the anode cylinder 3 was not accelerated and thus cooling efficiency could not be improved.
In the drawings of the above-mentioned JP 10-269953 A and other references, an anode cylinder is in contact with upper and lower pole pieces. However, one end of the anode cylinder needs to be free when the distance between the pole pieces is set precisely, as described above.
To reduce heat resistance in the anode part and facilitate cooling, enlarging the cross-sectional area of the anode components such as the vanes 2 and the anode cylinder 3 can be considered. However, this affects a high frequency characteristic, and thus there is a limit in doing so. For example, there occurs a problem that the degree of coupling with the outer cavity 60 through the slot 4 becomes inadequate if the anode cylinder 3 is thickened. Therefore, the peak oscillation output generated by the magnetron is limited due to the limit of heat release of the anode part.
For the above reasons, to achieve heat release as much as possible, it is proposed that the cooling passage 11 is provided at the base of the anode cylinder 3 on the side of the input side structure 14 to run a coolant therethrough for cooling, as shown in FIG. 6, but even by this cooling, there is a limit of heat release.